The proposed research consists of an interrelated series of experiments designed to study the influences of several blood alcohol concentrations upon certain key perceptual-cognitive functions which are assumed to be especially crucial for successful automobile driving. One set of studies is concerned with alcohol and divided attention, i.e., the influences of alcohol, signal probability and spatial location, and difficulty of concurrent fixation task upon reaction time. A second set is concerned with alcohol and the speed and accuracy of perceptual identification of simple and complex meaningful stimuli, e.g., the influences of alcohol and the associative reaction time and affective value of tachistoscopically presented words upon identification accuracy and thresholds. A third set involves the influences of alcohol and of marijuana upon information processing in terms of stimulus and response certainty and uncertainty in visual pattern-recognition tasks. The fourth set is concerned with the influences of alcohol upon visual search in terms of eye movements, stimulus uncertainty, and selective attention. The fifth set is concerned with the influences of alcohol upon selected physiological variables, i.e., body temperature and muscle tension, as well as variations attributable to differences in time of day.